Glucocorticosteroids are growth-modulating hormones for cells in tissue culture. However, since the biochemical basis for their growth-modulation is unknown, their action on different cell types is unpredictable. Often neoplastic transformation alters the cellular response to these hormones. For instance, they stimulate cell proliferation in the untransformed mouse fibroblast cell line (3T3, but they suppress cell growth in its simian virus 40-transformed derivative, SV3T3, in either serum-containing or serum-free media. This growth suppression is dependent on the presence in the medium of biotin, a cofactor for a key gluconeogenic enzyme, pyruvate carboxylase. This application seeks to understand the biochemical mechanism of SV3T3 growth suppression by testing the hypothesis that suppression is a consequence of the inhibition by glucocorticoids of glucose and glutamine catabolism (i.e. inhibition of glucose uptake and degradation, reduction in glutamine oxidation, and a stimulation of gluconeogenesis) with possibly a decline in cellular ATP. The experimental approach is to measure directly the effect of glucocorticoids on these biochemical parameters in both 3T3 and SV3T3 cells under various culture conditions (e.g. + serum, + biotin, + hormones, etc). Measurements of glucose uptake and catabolism and gluconeogenesis will be made by radioactive tracer (14C) analysis. In addition, the specific activities of key gluconeogenic enzymes and the cellular ATP level will also be assayed. These experiments should yield a number of scientifically important findings: 1) a biochemical explanation of growth suppression by glucocorticoids in a virally-transformed cell line, 2) the documentation of fundamental differences in the regulation of carbohydrate metabolism and energy production and maintenance in untransformed vs. neoplastic cells, and 3) valuable information leading to the logical use of glucocorticoids in the development of serum-free media.